Ground fault circuit interrupter

ABSTRACT

A ground fault circuit interrupter and/or indicator comprising a relay switch and/or indicator lamp connected on one side to the grounded frame of an appliance or other part, and on the other side to the neutral wire or to the grounding wire of the electrical service. Current leaking from the hot line to the appliance frame due to moisture or faulty insulation passes through the relay coil and/or indicator to the neutral line or grounding wire of the service, and this actuates the relay switch to open the hot line circuit to the appliance. In one embodiment, there is an additional circuit breaker in the hot line comprising a relay switch serially connected to the hot line, which is energized by excessive current flow, as in a line-to-line short.

Adamo 41 GROUND FAULT CIRCUIT INTERRUPTER [76] inventor: Daniel M.Adamo, 125 E. vCrescent Avenue, Redlands, Calif. 92373 [22] Filed: May27, 1971 [21] Appl.No.: 147,516

[52] US. Cl. "317/18 A, 317/13 R, 317/40 A,

340/255 [51 Int. Cl. ..H02h 3/16 [58] Fieldol Search ..3l7/l8 A,40A, 13R; 340/255 {56] I References Cited UNITED STATES PATENTS 3,171,0622/1965 Rowe. ..3l7/18 A 3,562,588 2/1971 Zielasko ...317/l8 A 3,402,3269/1968 Guasco et a1. ..3 17/18 A [451 Apr. 17, 1973 FOREIGN PATENTS ORAPPLICATIONS 599,113 6/1934 eem ..'..."..I.......'3i7 1s A PrimaryExaminer-James D. Trammell I Attorney-Herbert E. Kidder ABSTRACT Aground fault circuit interrupter and/or indicator comprising a relayswitch and/or indicator lamp connected on one Side to the grounded frameof an appliance or other part, and on the other side to the neutral wireor to the grounding wire of the electrical service. Current leaking fromthe hot line to the appliance frame due to moisture or faulty insulationpasses through the relay coil and/or indicator to the neutral line orgrounding wire of the service, and this actuates the relay switch toopen the hot line circuit to the appliance. in one embodiment, there isan additional circuit breaker in the hot line comprising a relay switchserially connected to the hot line, which is energized by excessivecurrent flow, as in a Iine-to-line short.

3 Claims, 6 Drawing Figures SHEET 1 0F 2 PATENTEB APR 1 71973 '0 m mw vrE N M w GROUND FAULT CIRCUIT INTERRUP'IER BACKGROUND OF THE INVENTIONThe present invention relates generally to circuit interrupters, andmore particularly to a device for detecting the existence of currentleakage from the hot line to the frame of an appliance or other part,having an electrical connection to the grounding wire of the service,and which functions to open the hot line circuit so that the applianceframe is no longer electrified. Current leakage of the type referred tomay be caused by moisture or defective insulation, particularly in motorcoils, and may cause the appliance frame to be electrified even thoughthe on-off switch of the appliance may be turned off. If the groundingconnections should be inadequate due to corrosion of the connections,oxidation of the water pipes, excessive dryness of the soil, or anyother cause, this results in an extremely dangerous condition, wherein aperson may be electrocuted by touching the frame while in contact with agrounded, or return conductor.

The danger is caused by the fact that grounding appliance frames to theneutral conductor of the electrical service, as required by theelectrical codes, provides a readily available link between a livecircuit and an earth ground at any point where a ground connection isavailable. The basic purpose of grounding appliances is to keep allnormally accessible metal parts at or near ground potential, to thatthere is never any appreciable voltage between the metal parts and theearth, or other objects connected directly to the earth.

The major advantage of grounding appliances is that grounding issupposed to prevent persons from receiving a shock from an appliancethat is effectively grounded, unless they contact a part intended tocarry current and a grounded surface. However, grounded appliancesenlarge the area and the locations at which persons can establishelectrical contact with the earth. This increases probability of shockfrom accidental contact with a live part, and increases probability ofshock from contact with an ungrounded metal part of an old ungroundedappliance that has developed a fault which causes the frame of theappliance to be electrically hot.

The major problem associated with grounding of appliances is that alarge number of homes are not equipped with three-prong groundedreceptacles, and therefore most customers who buy a new groundedappliance are faced with an installation problem. Oftentimes, thecustomer solves the problem by breaking off the ground plug, whichdefeats the grounding system. This produces an extremely hazardouscondition, because of the electrical interconnection of all dead metalparts within the appliance which causes the entire appliance to beelectrified if there should be a short or other electrical leakagewithin the motor. If a person were to touch an appliance having acircuit fault of the type mentioned, while in contact with a water pipeor gas pipe, he would receive, at the very least, a serious electricalshock and possibly be electrocuted. Service men, in particular, are aptto be endangered while working on grounded appliances that are notproperly connected to the grounding wire of the service line, or whileworking on grounded appliances that have developed a hot-line-to-frameshort. In the case of an appliance having a hot-line-to-frame short, theservice man may find that a motor or other electrical component burnsout before he can ascertainvwhere and what the trouble is, with theresult that the customer is faced with considerable added expense torepair damage that occurs after the service manhas started to work onthe appliance.

SUMMARY OF THE INVENTION The primary object of the invention is toprovide a new and improved ground fault circuit interrupter, that willautomatically indicate the existence of a ground fault (i.e.,hot-line-to-frame short) in any electrical appliance or circuit, eithera.c. or d.c., and instantaneously opens the circuit of the hot line,thereby stopping the current leakage to prevent any damage to thecircuit or injury to any person in contact with the appliance frame andthe ground.

Another object of the invention is to provide a device of the classdescribed, which additionally includes a circuit breaker that opens thecircuit of the hot line responsive to an excessive current flow, as whenthere is a direct line-to-line short in the system.

A further object of the invention in one of its embodiments is toprovide a ground fault circuit interrupter of the class described whichis contained within a plug connected between the service line and theappliance; said plug being either a three-prong and threesocket devicefor connecting a grounded appliance to a three-conductor service linehaving a grounding wire, or a two-prong and three-socket device forconnecting a grounded appliance to a two-conductor service line havingno grounding wire.

Still a further object of the invention in another of its embodiments isto provide a simple plug-in device that can be connected between theservice line and the appliance, which indicates the presence of a groundfault without interrupting the circuit of the hot line; said devicebeing either a three-prong three-socket unit or a two-prong three-socketunit, so as to permit connection of a grounded appliance to either athree-conductor or two-conductor service line.

These and other objects and advantages of the present invention willbecome apparent to those skilled in the art from a consideration of thefollowing detailed description of certain illustrative embodimentsthereof, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic drawing of aground fault circuit interrupter embodying the principles of theinvention;

FIG. 2 is a similar drawing of another embodiment of the inventionhaving a circuit interrupter for the hot line which is actuated by anoverload current; as when FIG. 5 shows a simplified version of theinvention, consisting of a ground fault indicator, without the circuitinterrupter, in a plug-in device adapted for connection between agrounded appliance and a three-conductor service line; and

FIG. 6 shows a plug-in device similar to that shown in FIG. 5, butadapted for connection between a grounded appliance and a two-conductorservice line.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIGv 1 of the drawings, theground fault circuit interrupter of the invention is designated in itsentirety by the reference numeral 10, and is adapted to be con nectedbetween a three-conductor grounded electrical service 12 and a groundedappliance 14. The service 12 comprises a hot line 16, neutral line 18,and grounding wire 20. Electrical codes require that the neutral line 18be connected to the grounding wire 20, and that the grounding wire beconnected to the water pipes or to a grounding rod buried deeply in thesoil. Appliance 14 comprises a frame 22, motor (or other electricalcircuit) 24, and electrical conductors 26,28 and 30. Conductor 26 is thehot line conductor; 28 is the neutral line conductor; and 30 is thegrounding wire conductor. All metal parts in the appliance are groundedto the frame 22, and the frame is electrically connected at 29 to thegrounding wire conductor 30.

The ground fault circuit interrupter may be built into the appliance 14,or it may be an entirely separate unit as shown in the drawing, in whichcase the circuit will be enclosed within a housing 32 and have one setof conductors 34, 36 and 38 connected to service lines 16,18 and 20,respectively, and another set of conductors 40 and 42 connected toappliance lines 26 and 30, respectively. Conductor 36 passes directlythrough the housing and is connected at its other end to the applianceneutral line 28. The housing 32 is electrically connected at 43 to thegrounding conductor 38.

Contained within the housing 32 are two relay switches 44 and 46. Relayswitch 44 has an electromagnet coil 48, which is connected at one end tohot line conductor 34, and at the other end to a wire 50. Wire 50 isfused at 52 and is connected to one end of a loadlimiting resistor 54,the other end of which is connected to the movable contact member 56 ofa single pole double throw relay switch 46. Contact member 56 isnormally closed to a stationary contact 58, which is connected to hotline conductor 40 going to the appliance 14. Contact 56 of relay 46 ismovable from contact 58 to a second contact 59 by an electromagnet coil60, one end of which is connected to grounding wire conductor 38, whilethe other end is connected to the grounding wire conductor 42 going tothe appliance. Switch contact 59 is connected by a wire 61 to anindicator lamp 62 which is connected, in turn, to the neutral conductor36. Thus, when switch member 56 is closed to contact 59, the lamp 62 islighted up.

In relay switch 44, the electromagnet coil 48 is operatively connectedto a movable switch member 64, and moves the same between open andclosed positions with respect to stationary contact 66. Switch member 64is connected to hot line conductor 34, and stationary contact 66 isconnected by a line '68 to wire 42. Also connected to contact 66 is awire 69 going to neutral conductor 36, and serially connected into thewire is an indicator lamp 70.

The operation of this embodiment of the invention is as follows: Duringnormal operation of the appliance 14, when everything is in good workingorder, electrical current to operate the motor 24 passes from hot line26 to neutral line 28, and there is no current passing through thegrounding wire 30. Current passes from the service hot line 16 throughconductor 34, coil 48, fuse 52, resistor 54, contacts 56 and 58 of relayswitch 46, and via conductor 40 to the appliance hot line 26. At thesame time, the return circuit carries current from neutral line 28,through conductor 36 to the neutral service line 18. Since there is nocurrent passing through the appliance grounding wire 30, there is nocurrent passing through those parts of the circuit interrupter whichconnect line 42 to line 38. With no current passing through lines 42 and68 the indicator lamps 62 and remain dark.

However, in the event that moisture or faulty insulation causes currentto leak from hot line 26 to the frame 22 of the appliance, the followinghappens: Current passes through grounding wire 30 of the appliance toconductor 42, through electromagnet coil 60 to conductor 38, and thenceto the grounding wire conductor 20 of the service line. At the sametime, part of the current in conductor 42 is shunted through lines 68,69 and lamp 70, to neutral conductor 36, thereby causing lamp 70 tolight up. Current passing through coil 60 energizes the latter, causingswitch member 56 to be pulled away from contact 58, and into engagementwith contact 59. As a result, the circuit from the hot line 16 to theappliance 14 is opened, and this immediately stops the electricalleakage, as the appliance 14 is then effectively cut off fromallelectricity. At the same time, lamp 62 is lighted up and remainslighted, notifying the repairman that a ground fault has caused thedevice to shut off the current to the appliance. After the ground faulthas been corrected, the switch member 56 can be reset manually tocontact 58. If the leakage current should be extremely weak, owing tomoisture or some other high-resistance short, the amount of current maynot be enough to actuate the relay switch 46, but indicator lamp 70 willstill light up, showing that there is a small ground fault in theappliance that should be taken into account. Preferably the indicatorlamps 62 and 70 are neon glow lamps, which require very little currentto light them up.

If there should be a sudden overload in the system, due to aline-to-line short, the increased current passing through the hot lineconductors 34, 50, 46-, causes the electromagnet coil 48 to be energizedsufficiently to close movable contact 64 against stationary contact 66,thereby sending current from hot line 34 through line 68, coil 60, andline 38, to the grounding wire 20 of the electrical service. This lightsup the indicator lamp 70 and also energizes electromagnet 60 to moveswitch member 56 from contact 58 to contact 59, thereby interrupting thehot line circuit to the appliance, and at the same time lighting up lamp62. Coil 48 and resistor 54 are selected to have the characteristic ofclosing relay switch 44 only when the current load exceeds the maximumcurrent drawn by the appliance 14 when everything is in good workingorder. Thus, the momentary surge of current when motor 24 starts up isinsufficient to energize the relay 44, but any overload currentappreciably in excess of the starting current will cause the relay 44 toclose switch member 64 to contact 66, and interrupt the circuit. Relay44 thus acts in the same manner as a circuit breaker, except that it canbe set to interrupt the current at a lower current level than the usualto ampere circuit breaker. When the unit 10 has been triggered by adirect line-to-line short in the appliance 14, this condition isindicated by the fact that both lamps 62 and 70 are lighted up.

Another embodiment of the invention is shown in FIG. 2, wherein partsthat correspond to parts already described in connection with FIG. 1have the same reference numerals as in the latter, but with the primesuffix. The unit of FIG. 2 is designated in its entirety by thereference numeral 10, and comprises a housing 32' containing relayswitches 72, 74, and 76, which cooperate to perform the same functionsas relays 44 and 46 in FIG. 1. Relay switch 72 is a ground fault circuitinterrupter having a movable member 78 that is normally closed against astationary contact 80. Switch member 78 is connected to hot line wire34' and contact 80 is connected to a conductor 82. An electromagnet coil84 is serially connected between grounding wire conductors 38' and 42',and is energized by leakage current passing along these conductors fromgrounding wire 30 on the appliance to 20 in the electrical service. Whencoil 84 is energized, switch member 78 is pulled away from contact 80,and closed to another contact 85, opening the hot line circuit to theappliance and simultaneously sending current along a wire 87 togrounding conductor 42 and thence through an indicator lamp 89 toneutral conductor 36. Relay switch 72 thus corresponds to relay switch46 of FIG. 1, in that they both operate to open the hot line circuitresponsive to current passing through the grounding wires of the system.Lamp 89 lights up to show that the unit 10' has been triggered by aground fault in appliance 14, and corresponds to lamp 62 in FIG. 1.

Relay switch 74 comprises a movable member 86 that is connected to hotline wire 82; stationary contact 88 that is connected to resistor 54';and electromagnet coil 90 that is serially connected between neutralwire 36 and movable member 92 of relay switch 76. To complete thepicture, relay switch 76 has a stationary contact 94 and anelectromagnet coil 96, the latter being serially connected betweenresistor 54' and hot line wire 98. Wire 98 is connected to wire 40 by afuse 52, and stationary contact 94 is connected to wire 98 by a wire100. Switch member 92 is normally open with respect to contact 94, butis closed to the latter by electromagnet coil 96 when the excessiveoverload current surges through the hot line wires as a result of adirect line-to-line short in the appliance. Closing switch contacts 92,94 sends current from hot line wire 98 to electromagnet coil 90 in relayswitch 74, opening contacts 86, 88 and thereby interrupting the hot linecircuit to the appliance. Thus, relay switches 74 and 76 cooperate toopen the hot line circuit responsive to an excessive current, and aretherefore functionally equivalent to the combined relay switches 44 and46 of FIG. 1. An indicator lamp 101 is connected between hot line 34'and neutral line 36' to indicate that the electrical service 12 is aliveand that there is current coming into the unit through the lines 34' and36.

The mode of operation is essentiallythe same with the embodiment of FIG.2 as it is in FIG. 1. Leakage current in the appliance 14 due to aground fault, energizes relay switch 72 to open the hot line circuit andcause lamp 89 to light up. Overload current due to line to-line short inthe appliance causes relay switch 76 to close member 92 to contact 94,thereby energizing relay switch 74 to open the hot line circuit. In bothof the embodiments of FIGS. 1 and 2, the hot line circuit may include acapacitor (not shown) connected in series with the resistor 54 or 54 toprovide an impedance that determines the amount of current required toenergize the relay (44 or 76) which actuates the circuit interrupter inthe hot line circuit responsive to an excessive overload current.

A third form of the invention is shown in FIG. 3. In this embodiment,the ground fault circuit interrupter is designated by the referencenumeral 102, and is incorporated in its simplest form into a plug 104having three prongs 106, 108 and 110 at one end, and sockets 112, 114and 116 at the other end. Prong 106 and socket 112 are part of the hotline; prong 108 and socket 114 are part of the grounding line; and prong110 and socket 116 are part of the neutral line. The neutral andgrounding lines are connected by a wire 117. Prongs 106, 108 and 110 areadapted to be inserted into any standard three-prong grounding typereceptacle (i.e., service line 12), while sockets 112, 114 and 116 areadapted to receive a standard threeprong grounding plug on the extensionwire of the appliance 14. The plug body 104 has an interior cavity 118,and contained within this cavity is a relay switch 120 consisting ofstationary contacts 122, 123; movable switch member 124; andelectromagnet coil 126. Stationary contact 122 is connected to socket112; movable member 124 is connected to prong 106; and electromagnetcoil 126 is connected serially between prong 108 and socket 114. Thesecond stationary contact 123 is connected by a wire 128 to a neon lamp130, and the lamp circuit is completed by a wire 132 going to theneutral wire connecting prong l 10 to socket 1 16.

Moveable switch member 124 is normally closed to stationary contact 122,thereby closing the hot line circuit to the appliance. Contact 123 isopen, and lamp is therefore dark when everything is in good workingorder. However, leakage current from the appliance frame 22, passingthrough grounding conductor 30, socket 114, electromagnet coil 126 toprong 108 and finally out through grounding outlet 20, causes the coil126 to open switch member 124 from contact 122 and close it to contact123. This interrupts the hot line circuit to the appliance, and causesthe lamp 130 to light up. A reset button 134 allows the repairman toreset the switch member 124 so that it is closed to contact 122 when thefault has been repaired.

FIG. 4 shows a similar plug-in circuit interrupter having two prongs106' and 110' that go into the hot line and neutral line sockets 16 and18 of a two-prong, ungrounded receptacle. At the other end of the plugare three sockets 112, 114' and 116, to receive the threepronged plug ofthe grounded appliance 14. In this case, movable switch member 124' isconnected to prong 106', and stationary contact 122' is connected tosocket 112'. Electromagnet coil 126' is connected at one end togrounding socket 1 14', and at the other end by a wire 134 to neutralprong 110. Contact 123' is connected by a wire 135 to a neon lamp 130',and the circuit of lamp 130' is completed by wire 132' to prong 110'.Leakage current from the appliance frame 22 passes through groundingwire 30, socket 114', electromagnet coil 126', wire 134, and out throughneutral prong 110 to neutral side 18 of the electrical outlet. Thisopens switch member 124 from contact 122 and closes it to contact 123',thereby opening the hot line circuit to the appliance and simultaneouslylighting up lamp 130. A reset button 134' allows the contact 124' to bereset after having been opened.

FIGS. and 6 show two plug-in models of the invention in its simplestform. FIG. 5 is a three-socket and three-prong plug, while FIG. 6 is athree-socket and two-prong adapter plug, for use in connecting agrounded appliance to a non-grounding receptacle. In each case, the unitis a warning device to let a repairman know that there is a groundfault, without actually interrupting the circuit. In FIG. 5, a warningneon lamp 136 is serially connected between grounding socket 114" andgrounding prong 108". Sockets 112" and 116" are connected directly totheir respective prongs 106" and 110". Leakage current due to a groundfault in the appliance 14 causes the lamp 136 to light up, warning therepairman that the appliance frame is electrically connected to the hotline, and suitable steps should be taken before proceeding further.

In FIG. 6, the two prongs 106" and 110" are connected to the hot lineand neutral socket 112" and 116", respectively. Grounding socket 114" isconnected to indicator lamp 136', which is also connected to prong 110'.Indicator lamp 136" is lighted up by leakage current from the applianceframe 22 through conductor 30, socket 114", lamp 136', prong 110", tothe neutral side of the electrical outlet.

While I have shown and described in considerable detail severalillustrative forms of my invention, it will be understood by thoseskilled in the art that the invention is not limited to such details,but might take various other forms. The invention works equally wellwith either a.c. or d.c. current, and may be used with any voltage.Moreover, it is not limited to three-prong grounding plugs andreceptacles, but might be used in any circuit (such as an automobile,for example) having a hot line and return line from the electricalsource to a grounded-frame appliance or motor, wherein the frame of theappliance is connected by a suitable conductor to the return line. Thus,the device of the invention will detect any current leakage from the hotline to the grounded frame of the appliance, and such leakage current isutilized to interrupt the hot line circuit to the appliance, so as tocut it off from the source of electricity and thereby eliminate anychance of injury or damage due to short circuit.

Iclaim:

1. A device for use with an electrical appliance having a grounded frameand including an electrical connection having a hot wire, neutral wire,and a grounding wire connected to said frame, said electrical connectionbeing connected to an electrical service consisting of a hot conductor,a neutral conductor, and a grounding conductor, said device comprising:

a hot line connecting said hot conductor of said electrical service tosaid hot wire of said appliance electrical connection; a neutral lineconnecting said neutral conductor of said electrical service to saidneutral wire of said appliance electrical connection;

a grounding line connected to said grounding wire of said applianceelectrical connection and to said grounding conductor of said electricalservice;

current-flow-interrupting means serially connected to said groundingline for opening the hot line responsive to the flow of leakage currentalong the grounding line due to the existence of a ground fault in saidappliance;

said current-flow-interrupting means comprising a normally-closed relayswitch in said hot line, said relay switch being opened by anelectromagnet serially connected between said grounding line and saidgrounding conductor of said electrical service.

2. A device for use with an electrical appliance having a grounded frameand including an electrical connection having a hot wire, neutral wire,and a grounding wire connected to said frame, said electrical connectionbeing connected to an electrical service consisting of a hot conductorand at least one return conductor means, said device comprising:

a hot line connecting said hot conductor of said electrical service tosaid hot wire of said appliance electrical connection;

a neutral line connecting said return conductor means of said electricalservice to said neutral wire of said appliance electrical connection;

a grounding line connected to said grounding wire of said applianceelectrical connection and to said return conductor means of saidelectrical service;

current-flow-detecting means serially connected to said grounding linefor detecting the flow of leakage along the grounding line due to theexistence of an electrical path from said hot wire to said applianceframe;

said current-flow-detecting means including a relay switch actuated bythe flow of leakage current along said grounding line to open thecircuit of said hot line, thereby interrupting the flow of current alongsaid hot line to said appliance; and

means actuated by an excessive overload current flow through saidhot-line to energize said relay switch.

3. A device as in claim 2, wherein the last-named means comprises asecond relay switch having normally open contacts connected to said hotline and to said first-named relay switch, respectively, said secondrelay switch being operable to close said normally open contacts andthereby send current from said hot line to said first-named relayswitch, so as to actuate the latter and open the hot line to saidappliance.

1. A device for use with an electrical appliance having a grounded frameand including an electrical connection having a hot wire, neutral wire,and a grounding wire connected to said frame, said electrical connectionbeing connected to an electrical service consisting of a hot conductor,a neutral conductor, and a grounding conductor, said device comprising:a hot line connecting said hot conductor of said electrical service tosaid hot wire of said appliance electrical connection; a neutral lineconnecting said neutral conductor of said electrical service to saidneutral wire of said appliance electrical connection; a grounding lineconnected to said grounding wire of said appliance electrical connectionand to said grounding conductor of said electrical service;current-flow-interrupting means serially connected to said groundingline for opening the hot line responsive to the flow of leakage currentalong the grounding line due to the existence of a ground fault in saidappliance; said current-flow-interrupting means comprising anormallyclosed relay switch in said hot line, said relay switch beingopened by an electromagnet serially connected between said groundingline and said grounding conductor of said electrical service.
 2. Adevice for use with an electrical appliance having a grounded frame andincluding an electrical connection having a hot wire, neutral wire, anda grounding wire connected to said frame, said electrical connectionbeing connected to an electrical service consisting of a hot conductorand at least one return conductor means, said device comprising: a hotline connecting said hot conductor of said electrical service to saidhot wire of said appliance electrical connection; a neutral lineconnecting said return conductor means of said electrical service tosaid neutral wire of said appliance electrical connection; a groundingline connected to said grounding wire of said appliance electricalconnection and to said return conductor means of said electricalservice; current-flow-detecting means serially connected to saidgrounding line for detecting the flow of leakage along the groundingline due to the existence of an electrical path from said hot wire tosaid appliance frame; said current-flow-detecting means including arelay switch actuated by the flow of leakage current along saidgrounding line to open the circuit of said hot line, therebyinterrupting the flow of current along said hot line to said appliance;and means actuated by an excessive overload current flow through saidhot line to energize said relay switch.
 3. A device as in claim 2,wherein the last-named means comprises a second relay switch havingnormally open contacts connected to said hot line and to saidfirst-named relay switch, respectively, said second relay switch beingoperable to close said normally open contacts and thereby send currentfrom said hot line to said first-named relay switch, so as to actuatethe latter and open the hot line to said appliance.